A DC breaker (direct current circuit breaker) is used to block a fault current when a fault occurs in a direct current line used as a high voltage transmission line. The direct current line used for a high voltage is used as a transmission line of a high voltage equal to or greater than 50 kV of a high voltage direct current (HVDC) transmission system or a distribution line of a middle voltage equal to or less than 50 kV of a middle voltage direct current distribution system.
The DC breaker is equipped with a mechanical switch to block a fault current when a fault occurs in the direct current line. The mechanical switch blocks the fault current by opening to prevent a system in which a fault occurs from affecting another system in normal state when a fault current is generated in a HVDC transmission system or a middle voltage direct current distribution system. The mechanical switch may have an arc generated when it is opened to block the fault current. Once the arc is generated, the fault current flows continuously via the arc, thereby damaging various elements of a system.
A related art to resolve problems described as above is disclosed in Korean Patent No. KR 1183508. The Korean Patent No. KR 1183508 relates to a current blocking device and is configured to include at least one interrupter, a surge arrester, and a resonant circuit.
Each of the one or more interrupters is used as a mechanical switch and has a plurality of contacts which are movable from a closing position to an opening position relative to each other to block a current entering through the interrupter which is disposed in a first current path. The surge arrester is connected to the resonant circuit in parallel, starts to send a current when a voltage being applied to the interrupter during the separation of the contacts reaches a predetermined value, and allows a direct current to flow as a result of existence of a voltage applied to the interrupter of the first current path until the direct current changes a direction to a second current path connected to the first current path. The resonant circuit is connected to the interrupter in parallel, is configured to include a capacitor and an inductor which are connected in series, and generates an oscillating current overlapping with the direct current to be able to block the current entering through the interrupter by allowing the current entering through the interrupter to become zero when the contacts are separated.
A conventional DC breaker such as the Korean Patent No. KR 1183508 has a problem that determination of charging direction of a charging voltage being charged into the capacitor of the resonant circuit is limited and a control time cannot be also determined in the case of supplying the oscillating current to the interrupter.